Filter device

ABSTRACT

The invention relates to a filter device with a filter housing ( 10 ) and a first filter element ( 12 ), arranged therein through which a medium may flow in a given direction and with a bypass device ( 22 ). Along with the first filter element ( 12 ), a further second filter element ( 32 ) is provided, said filter elements ( 32 ) are arranged in series, one behind the other, in the direction of flow and, on the bypass device ( 22 ) being activated, the further filter element ( 32 ), immediately following in the direction of flow, carries out a filtration of the medium. The further filter element thus takes over the main filtration of the medium on actuation and operation of the bypass device as the first filter element is essentially no longer available for a filtration process due to the bypass device.

[0001] The invention relates to a filter device with the features of the preamble of claim 1.

[0002] Comparable filter devices (FR-A-1 415 943, U.S. Pat. No. 3,000,505) are known in a plurality of embodiments and sizes. Within the filter housing there is generally at least one hollow-cylindrical filter element which removes impurities from fouled liquid supplied by way of an inlet into the filter housing, flow taking place through the respective filter element from the outside to the inside and the filtering filter mat of the filter element being supported along a support tube which is provided with passages. The liquid which has been filtered in this way is then drained by way of an outlet in the filter housing for further use. The longer the filter element is in operation for filtration, the more it is clogged by dirt until finally the filter element forms an almost impassable barrier for the fluid flow (medium) and the latter no longer reaches the outlet side of the filter housing. To avoid interruption of the fluid flow in question, which may result in the shutdown of an entire hydraulic system, for example DE 195 46 440 A1 has suggested for example providing within the filter device with the filter housing a bypass valve as a so-called bypass device which has a spring-loaded closing part which finally opens with increasing fluid pressure within the filter housing and clears a fluid-carrying path with disconnection of the filter element directly from the inlet to the outlet. The fluid or the medium consequently no longer flows through the filter element with a definable radial direction, but the fluid flow moves outside the filter element essentially in the axial flow direction in the space between the outside periphery of the filter element and the inside periphery of the filter housing and the fluid flow which has been deflected in this way then passes by way of the bypass valve without a filtration process through the interior of the filter element and is discharged to the outlet point. These bypass valves or other comparable bypass device are accordingly used for operating reliability and to prevent unwanted pressure rises; this can otherwise lead to damage within the hydraulic system.

[0003] U.S. Pat. No. 5,888,383 discloses a generic filter device with a filter housing and a first filter element which is located therein, which extends along the middle lengthwise axis of the filter housing, and through which flow of a medium takes place with a definable direction from one fluid inlet to one fluid outlet, and with a bypass device (bypass valve), in addition to the first filter element there being another, second filter element, the respective filter elements being located in succession in the flow direction, when the bypass device takes effect the other filter element which directly follows in the flow direction undertaking filtration of the medium, one filter element extending essentially over the entire structural length of the filter housing and the other filter element projecting with its end cap with a reduced overall length into the one filter element.

[0004] The embodiment as shown in FIG. 2 of the indicated US document moreover discloses choosing for one filter element one with high filter mesh fineness and for the other filter element which projects into it, one with coarser filter mesh fineness. This results in that with the one filter element which lies to the outside primary filtration and consequently also fine filtration are undertaken and only when the first filter element has been clogged by dirt does the bypass device (bypass valve) open and the other filter element which follows in the flow direction then undertakes coarse filtration of the medium such that in any case damage to the following hydraulic circuit is precluded.

[0005] In the known approach the installation length of the other filter element extends essentially over the entire length of the first filter element and the outside periphery of the other filter element on the filter mat structure side is surrounded on the outer peripheral side by a closed cylindrical protective jacket which, on its bottom side which faces the fluid inlet and outlet which in the axial direction toward the middle lengthwise axis of the filter housing enter the latter on the bottom side, has a radial distance over which the fluid which is to be filtered, originating from the bypass device (bypass valve) is delivered to coarse filtration by the other filter element. The indicated protective jacket stiffens the other filter element so that it is for the most part stable relative to pressure peaks, especially also relative to the fluid inlet side, and otherwise the indicated protective jacket prevents unwanted washing out of the dirt particles collected in the other filter element onto the clean side of the filter device; solely due to the protective jacket and the axial alignment of the fluid inlets parallel to the middle lengthwise axis of the filter housing do unfavorable flow conditions arise; this adversely affects filtration performance with the known device in normal filter operation and the attachment of the protective jacket requires on the one hand installation space within the filter device and on the other leads to corresponding additional costs in production and maintenance.

[0006] On the basis of this state of the art the object of the invention is to further improve the known filter devices with a bypass device while maintaining the advantages in the prior art, specifically that even in the case of triggering of the bypass device (bypass) damage of any type to the overall hydraulic system is avoided such that an especially compressively-stiff structure for the entire filter element configuration is ensured, that the flow conditions in filter operation are favorable with simultaneously low production and maintenance costs. The object in this respect is achieved by a filter device with the features of claim 1.

[0007] In that, as specified in the characterizing part of claim 1, the other filter element has an installation length which is shortened by at least one half compared to the first filter element and because the second filter element projects into the first filter element to the extent that its top end cap lies essentially in one plane transversely to the middle lengthwise axis with the top end of the fluid inlet which extends laterally through the filter housing, there is an especially compressively-stiff structure for the entire filter element configuration with respect to the radial inflow of the medium to be filtered by way of the fluid inlet. Since this compressively-stiff structure is implemented without further aids, such as a protective jacket or the like, the production costs and maintenance costs are reduced accordingly when the filter elements are replaced by new ones. The medium which is to be filtered flows through the first filter element essentially in the radial direction, originating from the fluid inlet on the side filter housing, and travels filtered in this way to the other, second filter element. As a result of the radial direction of flow through the filter elements the flow conditions are favorable for the fluid which is to be filtered within the filter element system. Furthermore, the pertinent configuration with different overall lengths enables compact accommodation of the bypass valve in the end area of the first filter element.

[0008] The configuration is such that with the triggering and opening of the bypass device (bypass) the second filter element directly undertakes filtration of the fouled medium, so that primary filtration shifted to the second filter element can take place at the same time. Connecting the two filter elements in succession in the conventional flow direction of the medium moreover ensures that in case of failure of the first filter element which is otherwise available for primary filtration, for example in the case of bursting or when the filter mat tears or the like, the following additional filter element ensures filtration so that in the pertinent case dirt cannot enter the hydraulic circuit and cause damage. These safety functions play an important role especially when these filter elements are used in the area of bearing lubrication in wind power plants, in high rotation paper printing machines or the like.

[0009] In one especially preferred embodiment of the filter element as claimed in the invention, the first filter element has higher filter mesh fineness than the second filter element. The first filter element in the flow direction is therefore able to remove both extremely fine and also coarse dirt from the fluid flow and the medium and in case of failure it is then at least possible to separate the coarse dirt from the fluid flow by way of the second filter element.

[0010] In another, especially preferred embodiment of the filter device as claimed in the invention, the two filter elements are arranged coaxially to one another and extend along the middle lengthwise axis of the filter housing. This yields an overall filter device with a very compact structure and the two filter elements can be easily and quickly replaced in the sense of a modularly structured replacement set as a whole; this reduces production costs and also maintenance costs.

[0011] The bypass device by preference is a bypass valve which has a spring-loaded closing part which in its closed position blocks the fluid-carrying path within the two filter elements from one fluid inlet within the filter housing to the fluid outlet located therein and otherwise clears it. The bypass device could otherwise be formed from some other blocking part, a choke point or the like. Preferably, for adjusting the pretensioning of the spring and the opening force for the closing part there is a setting means which acts on the effective length of the respective closing spring.

[0012] In addition to the two indicated filter elements, it could be provided moreover that a third or additional filter element be used, the filter element which comes before in the flow direction having a bypass device and the filter mesh fineness accordingly decreasing from the preceding filter element to the following filter element. A finer filter element is therefore always connected upstream of the coarser filter element in the conventional flow direction.

[0013] When using two filter elements it has proven especially advantageous to provide the first filter element with a filter mesh fineness of 10 μm and to equip the second filter element which follows in the flow direction with a filter mesh fineness of approximately 200 μm.

[0014] The filter device as claimed in the invention is detailed below using the drawings.

[0015] The sole FIGURE shows schematically and not to scale the filter device as claimed in the invention, partially in a projection, partially in a lengthwise section.

[0016] The filter device has a filter housing which is designated as a whole as 10. In the filter housing 10 there is a first filter element 12. The filter element 12 forms a type of hollow cylinder and the filter mat 14 is pleated in the conventional manner which is not shown and encompasses a support tube 16 with fluid passages, the support tube 16 itself being made as a hollow cylinder. The pertinent support tube configuration ensures that for the direction of flow through the first filter element 12 from the outside to the inside the filter mat 14 can be effectively supported on the support tube 16 and for example does not bulge to the inside and possibly begin to tear. On the two ends of the filter element 12 said filter element is provided with end caps 18, 20, by way of which the filter element 12 is held accordingly within the filter housing 10. The respective end caps 18, 20 are connected fluid-tight to one another by way of the corresponding cementing and/or sealing means with the free ends both of the support tube 16 and also of the filter mat 14 of the first filter element 12.

[0017] As is to be seen in the line of sight to the FIGURE, within the filter device and in the area of the top end of the first filter element 12 there is a bypass device in the manner of a bypass valve which is designated as a whole as 22. It has a dome-shaped closing part 24 on which a closing spring 26 acts. The closing spring 26 is made in the manner of a compression spring which in the FIGURE keeps the closing part 24 in closing contact with a definable closing force with pretensioning. The cylindrical closing spring 26 which is made as a helical spring has an essentially linear spring characteristic, but for example can also have a progressive characteristic if made conical. In addition, a plurality of spring elements (not shown) can be arranged in succession or connected in parallel by one closing spring surrounding the other one on the peripheral side in order to keep the closing part 24 in the unactuated position of the bypass device 22 in the closed position.

[0018] To adjust the spring pretension and the opening force for the closing part 24 there is an adjustment means which is designated as a whole as 28 and which changes the spring length and moreover the degree of effectiveness of the closing spring 26. For incremental adjustment of the pretensioning of the spring the adjustment means 28 has a lock 30 which can be moved along the retaining rods of a retaining cage and can be locked to them in definable catch positions. The indicated length of the closing spring 26 is fixed in the unactuated state of the bypass valve or the bypass device 22 by the distance between the closing part 24 and the respective top of the locking ring 30. By moving the locking ring 30 into the other catch position the pertinent distance and consequently the closing characteristic for the closing part 24 change. Conversely, with only one bypass device 22 a plurality of given pressure ranges for the pertinent filter devices can be covered. The pertinent bypass valve with its catch and locking possibilities is fundamentally known and described comprehensively in DE 195 46 440 A1 so that it is not detailed here and the bypass valve or the bypass device 22 is addressed below only to the extent that it is necessary for the understanding of the invention.

[0019] In addition to the first filter element 12, within the filter housing 10 there is another second filter element 32, the respective filter elements 12, 32 being located in succession in the flow direction as shown, and the second filter element 32 which follows directly in the flow direction performing solely filtration of the medium (fluid flow) when the bypass device 22 in the form of the bypass valve takes effect, i.e., when the closing part 24 is opened.

[0020] In order to ensure efficient operation of the filter device, it is moreover provided that the first filter element 12 has higher filter mesh fineness than the second filter element 32. In other words, the first filter element 12 performs both fine and also coarse filtration of the medium, i.e., dirt with both large and small particle sizes is filtered out of the flow of media. The medium flows through the first filter element 12 therefore essentially in the radial direction and travels filtered in this way to the second filter element 32 with less filter mesh fineness compared to the first filter element 12, so that in the pertinent operating situation the second filter element 32 does not constitute a significant flow barrier for the already filtered medium, since the filter mesh fineness of the second filter element 32 is not sufficient to offer an essentially high flow resistance to the flowing medium. The fluid medium which has already been effectively cleaned by the first filter element 12 therefore penetrates the second filter element 32 essentially unobstructed.

[0021] In terms of its basic concept the second filter element 32 is built comparably to the first filter element 12, i.e., the second filter element 32 likewise has a preferably pleated filter mat 34 which surrounds a support pipe 36 with fluid passages. Furthermore, the two ends of the second filter element 32 are terminally encompassed by comparable end caps 38, 40, the end cap 38 which is the top cap viewed in the line of sight to the FIGURE being completely closed, conversely the lower, second end cap 40 having a passage point 42 for the filtered medium.

[0022] As the FIGURE furthermore shows, the two filter elements 12, 32 are located coaxially to one another and extend along the middle lengthwise axis 44 of the filter housing 10. In addition, the bypass device 22 (bypass valve) is likewise made essentially rotationally symmetrical and the middle axis of the bypass device 22 is essentially congruent with the indicated middle lengthwise axis 44 of the filter housing 10.

[0023] As furthermore can be seen from the FIGURE, the first filter element 12 extends essentially over the entire length of the filter housing 10, conversely the other, second filter element 32 has an installation length which is shortened conversely by at least one half. The indicated filter housing 10 in its central area has two housing pipe sections 46, 48 which can be connected to one another and which, connectable to one another in the conventional manner, close the interior of the filter housing fluid-tight relative to the environment. Viewed in the line of sight to the FIGURE, the lower housing pipe section 48 on the right side has a fluid inlet 50 and on its bottom a fluid outlet 52 which is located coaxially to the middle lengthwise axis 44 of the filter housing 10.

[0024] The fouled filter medium flows into the filter device by way of the fluid inlet 50 and travels cleaned, i.e., filtered, from the fluid outlet 52 into the remaining hydraulic circuit (not shown) to which the filter device is connected. The second filter element 32 projects into the first filter element 12 to the extent that the top end cap 38 lies essentially in one plane transversely to the middle lengthwise axis 44 with the end of the filter inlet 50 which is the top end viewed in the line of sight to the FIGURE. The pertinent configuration yields an especially compressively-stiff structure for the entire filter element configuration relative to the inflow of the medium to be filtered by way of the fluid inlet 50. The fluid inlet 50 is otherwise made in the manner of a connecting flange in order to facilitate connection of the pipework or the like. Furthermore, by way of the fluid inlet 50 it is also possible to connect the filter device as an attachment to a hydraulic system at a later time. Furthermore, the filter element 32 on its end opposite the free end is supported by a plate-like holding means 54 which closes the fluid outlet of the filter device in the filter housing 10 except for the aforementioned passage point 42 and except for the fluid outlet 52.

[0025] The filter housing 10 with its two housing pipe sections 46, 48 is closed on the end side by way of cap-like pipe end sections 56, 58, the lower pipe end section 58 encompassing on the outer peripheral side the lower housing pipe section 48 and it can be screwed onto it to form a seal. The lower pipe end section 58 accordingly also clears the fluid outlet 52 to the outside and forms a connecting point for subsequent pipework which is not detailed or for another connection possibility. The top pipe end section 56 is provided with a handling aid in the form of handling links 60 on its free top side which facilitate screwing and unscrewing of the top pipe end section 56. On its inside the pipe end section 56 is provided with segment-like load transmission links 62 which project down and which in the area of the top end of the bypass device 22 can be brought into contact with them so that when the pipe end section 46 is screwed onto the top housing pipe section 46 the load transmission links 62 press the first filter element 12 down when viewed in the line of sight to the FIGURE and in this way ensure its position in the lower filter element receiver of the filter housing 10.

[0026] The load transmission links 62 are preferably interconnected in the manner of a ring body and accordingly can be made in one piece. Furthermore they encompass round contact segments 64 so that not only in the axial direction, but also in the radial direction transversely to the middle lengthwise axis 44 accurate guidance of the filter element 12 is achieved in the fixing process. By unscrewing the top pipe end section 56 it is furthermore easily possible to change both the first filter element 12 and also the second filter element 32 and with the corresponding fouling to replace the pertinent filter elements 12, 32 with new elements. The bypass device 22 in the manner of a bypass valve can be maintained as a part which is less subject to wear and can be integrated accordingly into a first filter element 12 which is to be newly inserted. Moreover it is possible, except for the filter elements 12, 32, to obtain the other components of the filter device; this reduces maintenance costs. The indicated structure moreover enables simple handling; this increases ease of maintenance of the pertinent devices.

[0027] For the sake of better understanding, the manner of operation of the filter device is detailed below. The fouled fluid or filter medium enters the interior of the filter housing 10 by way of the fluid inlet 50. The filter medium then flows through first filter element 12 essentially in the radial direction and the dirt which is in the filter medium remains in the pleated filter mat 14 of the filter element 12. The first filter element 12 has a filter mesh fineness of preferably 10 μm (equals particle diameter) so that both fine and also coarse dirt is captured by the filter element 12. The filter medium which has been filtered in this way then flows through the passages of the support pipe 16 into the interior of the first filter element 12. The second filter element 32 which is designed to be coarser then essentially does not constitute a flow barrier and the cleaned fluid likewise flows through the filter mat 34 of the second filter element 32 in the radial direction. Then, emergence takes place from the filter device for the cleaned fluid by way of the passage point 42 and the fluid outlet 52. The filtered medium then is available for recirculation in a hydraulic system or the like. In addition to the aforementioned fluids, also gases, polymer melts or the like can be cleaned in this way optionally with filter elements which have been made differently (not shown).

[0028] If at this point with continuing use of the filter device the filter mat 14 of the first filter element 12 is clogged by dirt, an increased differential pressure is formed outside and inside of the first filter element 12 and at a definable threshold value determined by the closing force of the closing spring 26 the closing part 24 of the bypass valve which represents the bypass device 22 opens. Now the filter medium which is no longer cleaned essentially flows through the bypass device 22 and in this way travels into the interior of the filter element 12. In this case the second filter element 32 performs primary filtration, i.e., the uncleaned filter medium passes through its pleated filter mat 34 and in this way is cleaned. But the second filter element 32 has a much coarser filter mesh fineness structure so that only coarse dirt is captured and dirt with extremely small particles can enter the hydraulic circuit. As a result of coarse filtration then it is however ensured that the extremely fine particles which have passed as dirt cannot disrupt or adversely affect operation of the hydraulic system (lubricant circuit or the like).

[0029] Furthermore, it is possible to provide the pertinent filter devices with so-called differential pressure displays so that when the differential pressure threshold value is reached, at which the bypass device 22 opens, an alarm or warning signal is delivered; this enables maintenance personnel to specifically replace the fouled filter element 12. With the filter device as claimed in the invention it however ensured that dirt which becomes dangerous at any rate can be kept away from the hydraulic circuit. 

1. A filter device with a filter housing (10) and a first filter element (12) which is located therein, which extends along the middle lengthwise axis (44) of the filter housing (10), and through which flow of a medium takes place with a definable direction from one fluid inlet (50) to one fluid outlet (52), and with a bypass device (22), in addition to the first filter element (12) there being another, second filter element (32), the respective filter elements (12, 32) being located in succession in the flow direction, when the bypass device (22) takes effect the other filter element (32) which directly follows in the flow direction undertaking filtration of the medium, one filter element (12) extending essentially over the entire structural length of the filter housing (10) and the other filter element (32) projecting with its end cap (38) with a reduced overall length into the one filter element (12), characterized in that the other filter element (32) has an installation length which is shortened by at least one half compared to the first filter element (12) and that the second filter element (32) projects into the first filter element (12) to the extent that its top end cap (38) lies essentially in one plane transversely to the middle lengthwise axis (44) with the top end of the fluid inlet (50) which extends laterally through the filter housing (10).
 2. The filter device as claimed in claim 1, wherein the first filter element (12) has higher filter mesh fineness than the second filter element (32).
 3. The filter device as claimed in claim 1 or 2, wherein the two filter elements (12, 32) arranged coaxially to one another extend along the middle lengthwise axis (44) of the filter housing (10).
 4. The filter device as claimed in one of claims 1 to 3, wherein the bypass device (22) is a bypass valve which has a spring-loaded closing part (24) which in its closed position blocks the fluid-carrying path within the two filter elements (12, 32) from the fluid inlet (50) within the valve housing (10) to the fluid outlet (52) located therein and otherwise clears it.
 5. The filter device as claimed in claim 4, wherein for adjusting the pretensioning of the spring and the opening force for the closing part (24) there is a setting means (28) which changes the length of the closing spring (26).
 6. The filter device as claimed in one of claims 1 to 5, wherein the first filter element (12) on its one end encompasses the bypass device (22) and in the area of its other end the second filter element (32) while maintaining a radial distance.
 7. The filter device as claimed in claim 6, wherein the second filter element (32) on its end opposite the free end is supported by a plate-like holding means (54) which closes the fluid outlet (52) in the filter housing (10) except for the passage point (42).
 8. The filter device as claimed in one of claims 1 to 7, wherein the filter housing (10) consists of two pipe sections (46, 48) which can be connected to one another and wherein the ends of the filter housing can be closed with pipe end sections (56, 58).
 9. The filter device as claimed in one of claims 2 to 8, wherein the first filter element (12) has a filter mesh fineness of 3 μm to 30 μm, preferably 10 μm, and wherein the second filter element (32) has a filter mesh fineness of 50 μm to 400 μm, preferably of 200 μm. 